Using rapid flow microfluorometry (FMF) for analysis and sorting of cells, aspects of the following projects have been supported during the previous year: (l) murine T-cell differentiation and recognition of foreign MHC determinants; (2) characterization of new lymphocyte differentiation antigens; (3) identification of suspopulations of human lymphocytes; (4) analysis of antibodies induced by anti-idiotypes; and (5) characterization of new dyes for FMF.